The small size and tunability of nanomaterials has engendered great interest in biological applications such as diagnostics and therapeutics. Silver and metal oxide nanoparticles show bactericidal effects in a range of microorganisms. Metal nanoparticles may act as infrared absorbers and induce cell death by heating the surrounding medium. This toxic effect is generally attributed to the generation of generic reactive oxidative species (ROS) and free radicals, which can damage biomolecules such as DNA, RNA and proteins.
Cells that grow in aerobic environments have mechanisms to mitigate or use ROS through redox homeostasis processes. Within cell types, a specific redox homeostasis is maintained by the cell, and this governs the function of broad processes including metabolism and signal transduction. The generation of the specific ROS species is determined by the redox environment present in the cell. Perturbation outside of a cells redox homeostasis is linked to cell death in Escherichia coli, cancer, cardiovascular disease, and ageing in humans, and irreversible tissue damage in plants.
Quantum dots (QDs) are nanoparticles made of semiconductor materials and small enough to exhibit quantum mechanical properties. Specifically, the QD's excitons are confined in all three spatial dimensions. Due to quantum confinement, QDs have quantized energy states that, when photo-excited, have excited electrons and holes available for interactions.
The electronic properties of QDs are intermediate between those of bulk semiconductors and of discrete molecules. Electronic characteristics of a QD are closely related to its size and shape. For example, the band gap in a QD, which determines the frequency range of emitted light, is inversely related to its size. In fluorescent dye applications, the frequency of emitted light increases as the size of the QD decreases. Consequently, the color of emitted light shifts from red to blue when the size of the quantum dot is made smaller. This allows the excitation and emission of QD to be highly tunable. Since the size of a QD may be set when it is made, its conductive properties may be carefully tuned and/or controlled. QD dot assemblies consisting of many different sizes, such as gradient multi-layer nanofilms, can thus exhibit a range of desirable emission properties.
There is a need in the art for novel compositions that can be used to promote growth and/or death of cells. In certain embodiments, the compositions promote selective growth and/or death of a cell type in the presence of another cell type. The present invention meets this need.